Electrolytic copper recovery method and electrolyte

ABSTRACT

High purity copper is recovered from the copper oxide containing ores by a continuous process wherein the copper is leached from the ore by an aqueous solution containing an inorganic acid, an oxidizing agent, a saturated water soluble aliphatic alcohol and a lignin sulfonic acid or salt thereof. After extraction, the copper containing leach solution is subjected to treatment in an electrolytic cell powered by a specially pulsed direct current wherein high purity copper is plated out at the cathode and the leach solution is recycled back for reuse in the extraction process.

United States Patent 1191 Pittman et a1.

[451 May 20, 1975 ELECTROLYTIC COPPER RECOVERY METHOD AND ELECTROLYTE [2]] Appl. No.: 458,887

[52] US. Cl. 204/108; 204/106; 204/107; 204/52 R; 106/1 [51] Int. Cl C22d l/16 [58] Field of Search 204/106-108, 204/52 R; 75/117; 106/1 [56] References Cited UNITED STATES PATENTS 617,911 1/1899 Smith et a1 204/108 2,579,551 12/1951 Corsini 204/108 2,769,775 11/1956 Schloen et al. 204/108 2,937,978 5/1960 Strauss et al. 204/52 R 3,535,218 lO/l970 Brown et al. 204/108 Primary Examiner-R. L. Andrews Attorney, Agent, or FirmCriddle & Thorpe [57] ABSTRACT High purity copper is recovered from the copper oxide containing ores by a continuous process wherein the copper is leached from the ore by an aqueous solution containing an inorganic acid, an oxidizing agent, a saturated water soluble aliphatic alcohol and a lignin sulfonic acid or salt thereof. After extraction, the copper containing leach solution is subjected to treatment in an electrolytic cell powered by a specially pulsed direct current wherein high purity copper is plated out at the cathode and the leach solution is recycled back for reuse in the extraction process.

9 Claims, No Drawings ELECTROLYTIC COPPER RECOVERY METHOD AND ELECTROLYTE BRIEF DESCRIPTION OF THE INVENTION This invention relates to the recovery of high purity copper from copper containing ores. More particularly this invention relates to the recovery of copper from copper containing ores by a novel process wherein the same solution serves as both a leaching solution and an electrolyte which may be reused over and over again after the copper has been recovered from the solution by means of a specially pulsed direct current applied at the electrodes.

Copper is known to exist in a combined state in nature in the form of a sulfide or as an oxidized material. The extraction of high purity copper from such ores has been both expensive and time consuming. For example, sulfide ores are generally pulverized and concentrated by flotation. The concentrate thus obtained is roasted in the presence of air to form a mixture of metal sulfides and oxides. The roasted mixture is heated in a furnace with limestone and sand. A slag mixture of calcium and ferrous silicates is disposed of and the resultant molten cuprous sulfide is then converted to copper by blasting air through the molten material. The copper thus obtained is impure and must be further refined electrolytically.

Oxidized copper ores, which may contain copper oxides, carbonates or mixtures thereof, have traditionally been treated with various strengths of sulfuric acid to leach out the copper. The resulting liquor containing the cupric ion is treated by metallic iron wherein the cupric ion is reduced and copper plated out on the iron as a sludge called cement copper.

Obvious disadvantages in the above described prior art processes are the multitude of steps required, result ing in high labor and equipment costs to produce copper which is only partially purified.

lmpure copper is further refined electrolytically by utilizing a high purity electrolytic solution of sulfuric acid and copper sulfate. The impure copper is used as the anode and high purity copper is obtained by plating out on sheets of thin high purity copper starter cathodes.

SUMMARY OF THE INVENTION It has now been found that high purity copper can be obtained from oxidized copper or a mixture of copper sulfide/oxidized copper ores without the need to resort to extensive concentration, smelting and refining operations. The entire operation is carried out in a leaching extraction cycle, followed by electrolytic deposition of purified copper at the cathode wherein the same solution is utilized for leaching and in the electrolytic bath. The electrolytic step is carried out utilizing a pulsed source of direct current power.

The leaching-electrolytic bath solution comprises an aqueous mixture containing (a) an inorganic acid, (b) an oxidizing agent, (c) a water soluble saturated aliphatic alcohol and a lignin sulfonic acid or salt thereof. While good results may be obtained by eliminating the oxidizing agent, alcohol or lignin sulfonic acid from the solution, all ingredients are necessary in order to obtain the optimum results desired. While it is not known just how each of the above ingredients functions in the mixture, and without being bound to any theory, it is believed that the oxidizing agent increases the yield of copper extracted from the ore and that the alcohol functions to stabilize the oxidizing agent, thereby prolonging its useful life. It is further believed that the lignin sulfonates or sulfonic acids act to refine the grain structure of the copper and allow for a more dense copper electro deposit.

The concentration of ingredients in the leachingelectrolyte solution may vary and optimum concentrations may be determined empirically for any given copper bearing ore. In general, it has been found that solutions containing from 10 to 1000 grams per liter of solution of inorganic acid; from 0.1 to 10 grams per liter of oxidizing agent, from 0.1 to 20 grams per liter of water soluble saturated aliphatic alcohol and-0.1 to 25 grams per liter of a lignin sulfonic acid or salt thereof are preferred.

Theoretically, any inorganic acid capable of leaching the copper from the ore and functioning as an electrolyte may be utilized. Principal among these acids are hydrochloric, nitric and sulfuric. Sulfuric acid is especially preferred.

Oxidizing agents which may be utilized in this invention include any compatible source having available oxygen, i.e., ozone, hydrogen peroxide, potassium permanganate and the like. The preferred oxidizing agent is hydrogen peroxide.

Any water soluble aliphatic alcohol which will stabilize the oxidizing agent may be used. Inclusive are both straight and branched carbon chains which may result in primary, secondary or tertiary alcohols. While monohydric alcohols are preferred diols and triols may also be used. By water soluble is meant those alcohols which are soluble in the aqueous leach-electrolyte solution in the concentrations in which they are used. In general, alcohols having from one to ten carbon atoms may be used with alcohols having from three to six carbon atoms being preferred. Exemplary of such alcohols are n-propyl, n-butyl and amyl alcohols.

Sulfonic acid derivatives of lignin are well known in the art. The free acid derivatives may be utilized in the practice of the present invention or one may use the acid salts thereof such as sodium ligno sulfonate and ammonium ligno sulfonate.

One advantage of the leaching-electrolyte solution as described herein is that it can be utilized in both steps of the copper recovery process and yet is not consumed in either step and can therefore be recycled. Obviously, this not only increases the economy of the operation but also considerably reduces pollution problems associated with spent liquor solutions. An additional advantage lies in the fact that copper sulfide ores can be treated and high purity copper obtained without the need to go through the expensive smelting operation which requires not only time and capital but great amounts of energy.

It has been found that the purity of the electrolytically deposited copper can be enhanced if the energy source used in this invention is a specially pulsed direct current. In general the pulse current is from 1.1 to 99.9 times the average current flowing between the electrodes. The pulses may be so timed that the current will flow from 0.01 to 1000.0 milliseconds at the maximum current and then from 0.01 to 1000.0 milliseconds at zero or reduced current. The rate of copper deposition at the cathode at any given copper ion concentration is a function of the current flow and time. In general, the average current density will be between 1 and amps per square foot with the pulse current varying from 1.1 to 100 times the average current.

The process is carried out by first crushing the copper bearing ore and then further reducing it in size so that the copper in the ore can be completely removed by the leaching solution. The ore is placed in the leaching solution for a period of time sufficient to dissolve all of the copper. The solution containing the copper ions is then filtered or otherwise treated to remove the undissolved materials and solution is pumped into an electrolytic cell wherein a pulsed direct current is applied and the purified copper plated out at the cathode. The solution depleted of the copper ion content is then recylced back to the leaching operation where it dissolves more copper.

The following examples serve to illustrate but not limit the claimed invention.

EXAMPLE 1 An aqueous leaching electrolyte solution having the following contents dissolved therein was prepared:

Sulfuric Acid 100 grams/liter n-Butyl Alcohol 1 grams/liter Hydrogen Peroxide 0.5 grams/liter Sodium Ligno Sulfonate l grams/liter Fifty gallons of the above solution was placed in a lead lined tank and 100 pounds of a finely ground copper oxide ore having a copper content of 3.1 percent by weight was added. The copper containing solution was then air agitated for a period of 18 minutes and then the pulsed direct current power supply was turned on and connected to a stainless steel cathode, the lead tank lining being used as the anode. The current pulse was set for 9.9 milliseconds on and 500 milliseconds off with the peak amperage being ten times the average.

current. The average current density was amps per square foot. The electroplating operation was continued until the copper was plated out of the solution. The resulting copper sheet deposited at the cathode was stripped, weighed and analyzed. The copper weighed 3.00 pounds and by analysis was found to be 99.85 percent pure.

EXAMPLE 2 A second aqueous leaching/electrolyte solution having the following contents dissolved therein was prepared:

Sulfuric Acid 80 grams/liter n-Propyl Alcohol 0.8 grams/liter Hydrogen Peroxide 0.8 grams/liter Ammonium Ligno Sulfonate 2 grams/liter One hundred twenty gallons of the above solution was added to one hundred pounds of ground copper ore containing 2.7 percent by weight copper in a lead lined leach tank. After ten minutes of mixing the pulsed direct current power supply was turned on and copper was deposited at the stainless steel cathode. The solution was continuously circulated through the circuit and after 27 hours the solution was analyzed and found to contain only 0.01 1 grams of copper per liter. The deposited copper was thus calculated to be 99.6% of the copper contained in the ore. The copper at the cathode was found by analysis to be 99.88% pure. During the electroplating operation the average current density was 25 amps per square foot, with the peak pulse amperage being 15 times the average and the pulse was set for 5.0 milliseconds on and 10.0 milliseconds off.

EXAMPLE 3 .The procedure of Example 1 was repeated with the exception being that the power for electroplating was furnished by a direct current generator with no pulsing. The deposited copper was found to be only 98.91 percent pure.

EXAMPLE 4 The procedure of Example 2 was repeated except that the hydrogen peroxide and n-propyl alcohol were omitted from the solution. The copper recovery was found to be only 97.6 percent. The recovered copper was 99.82 percent pure.

EXAMPLE 5 The procedure of Example 1 was again repeated except that the sodium ligno sulfonate was left out. The purity of the copper at the cathode was 99.83 percent and the recovery was 2.98 pounds. The deposited copper was not as smooth as in Example 1 and the deposit tended to be slightly powdery.

Although a preferred form of our invention has been herein disclosed, it is to be understood that the present disclosure is by way of example, and that variations are possible without departing from the subject matter coming within the scope of the following claims, which subject matter we regard as our invention.

We claim:

1. An electrolytic process for the recovery of high purity copper from copper containing ores which comprises the steps of (a) extracting copper from the ore in an aqueous solution containing from 10 to 1000 grams per liter of an inorganic acid; from 0.1 to 10 grams per liter of an oxidizing agent; from 0.1 to 20 grams per liter of a water soluble saturated aliphatic alcohol and from 0.1 to 25 grams per liter of a lignin sulfonic acid or salt thereof; and (b) subjecting the copper containing solution from step (a) to a pulsed direct current power source in an electrolytic cell wherein the pulse current is from 1.1 to 99.1 times the average current flow thereby depositing high purity copper at the cathode.

2. The process according to claim 1, wherein the inorganic acid is sulfuric acid.

3. The process according to claim 2, wherein the oxidizing agent is hydrogen peroxide.

4. The process accordingto claim 3, wherein the saturated alcohol is selected from the group consisting of propyl, butyl and amyl alcohols.

5. The process according to claim 4, wherein the solution contains a salt of a lignin sulfonic acid.

6. The process according to claim 1, wherein the copper depleted solution from step (b) is recylced back to step (a) for reuse in dissolving more copper.

7. The process according to claim 1, wherein the pulsed current operates from 0.01 to 1000 milliseconds at the pulse current and from 0.01 to 1000 milliseconds at zero or a reduced current.

8. A leaching/electrolyte solution for use in electrolytically recovering copper from copper containing ores comprising a water base having dissolved therein a mixture comprising 10 to 1000 grams per liter of an inorganic acid; from 0.1 to 10 grams per liter of an oxidizing agent; from 0.1 to 20 grams per liter of a water ide, the alcohol is selected from the group consisting of soluble saturated aliphatic alcohol and from 0.1 to 25 grams per liter of a lignin sulfonic acid or salt thereof.

9. The solution of claim 8, wherein the inorganic acid is sulfuric acid, the oxidizing agent is hydrogen perox- 5 propyl, butyl and amyl alcohols and the lignin acid is a ligno sulfonate salt. 

1. AN ELECTROLYTIC PROCESS FOR THE RECOVERY OF HIGH PURITY COPPER FROM COPPER CONTAINING ORES WHICH COMPRISES THE STEPS OF (A) EXTRACTING COPPER FROM THE ORE IN A AQUEOUS SOLUTION CONTAINING FROM 10 TO 1000 GRAMS PER LITER OF AN INORGANIC ACID; FROM 0.1 TO 10 GRAMS PER LITER OF AN OXIDIZING AGENT; FROM 0.1 TO 20 GRAMS PER LITER OF A WATER SOLUBLE SATURATED ALIPHATIC ALCOHOL AND FROM 0.1 TO 25 GRAMS PER LITER OF A LIGNIN SULFONIC ACID OR SALT THEREOF; AND (B9 SUBJECTING THE COPPER CONTAINING SOLUTION FROM STEP (A) TO A PULSED DIRECT CURRENT POWER SOURCE IN AN ELECTROLYTIC CELL WHEREIN THE PULSE CURRENT IF FORM 1.1 TO 99.1 TIMES THE AVERAGE CURRENT FLOW THEREBY DEPOSITING HIGH PURITY COPPER AT THE CATHODE.
 2. The process according to claim 1, wherein the inorganic acid is sulfuric acid.
 3. The process according to claim 2, wherein the oxidizing agent is hydrogen peroxide.
 4. The process according to claim 3, wherein the saturated alcohol is selected from the group consisting of propyl, butyl and amyl alcohols.
 5. The process according to claim 4, wherein the solution contains a salt of a lignin sulfonic acid.
 6. The process according to claim 1, wherein the copper depleted solution from step (b) is recylced back to step (a) for reuse in dissolving more copper.
 7. The process according to claim 1, wherein the pulsed current operates from 0.01 to 1000 milliseconds at the pulse current and from 0.01 to 1000 milliseconds at zero or a reduced current.
 8. A leaching/electrolyte solution for use in electrolytically recovering copper from copper containing ores comprising a water base having dissolved therein a mixture comprising 10 to 1000 grams per liter of an inorganic acid; from 0.1 to 10 grams per liter of an oxidizing agent; from 0.1 to 20 grams per liter of a water soluble saturated aliphatic alcohol and from 0.1 to 25 grams per liter of a lignin sulfonic acid or salt thereof.
 9. The solution of claim 8, wherein the inorganic acid is sulfuric acid, the oxidizing agent is hydrogen peroxide, the alcohol is selected from the group consisting of propyl, butyl and amyl alcohols and the lignin acid is a ligno sulfonate salt. 